Since the transmitting
station will not receive an explicit acknowledgement, it will increment its backoff stage
regardless of the fact that a collision occurred on the channel, or the frame was simply
corrupted by channel noise. Hence, in case of transmission impairments, the conditional
collision probability p, defined in the previous section as the probability that a transmitted
frame collides, now represent the union of the events i) the frame collided, and ii) the frame
was corrupted. In formulae:
(49)
As usual, ?„ represents the probability that a station transmits in a randomly chosen slot.
With this new definition of p, it becomes clear that the computation of ?„ is not affected.
Thus, Eq. (32) still holds and can be jointly solved with Eq. (49) to obtain the numerical
expressions for p and ?„.
( ) 1 1 1 1 ??’ ??’ ??’ ??’ = N ) ( p ?„ ?¶
Some additional care is required to compute the saturation throughput. In fact, it is
necessary to determine the proper probabilities of the various events that may occur on the
channel, events which now include the case of frame corruption. We can express the
throughput S as:
(50) ( )
( ) ( )c success idle e success s success idle
success
T P P T P T P P
] P [ E P S
??’ ??’ + + ??’ +
??’
=
1 1
1
?¶ ?¶ ??
?¶
where the probability Psuccess is still given by Eq.
Pages:
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262